1. Field of the Invention
The invention relates to a method for the control of an intersystem handover, in particular the handover between a GSM- and a UMTS mobile radio system.
2. Description of the Related Art
Reference is made to the UMTS standardization documents 3GPP: 3G TS 25.212 V3.1.1, 1999-12, Multiplexing and channel coding (FDD), 3GPP: 3G TS 25.222 V3.1.1, 1999-12, Multiplexing and channel coding (TDD), and 3GPP: 3G TS 25.331 V3.1.0, 2000-01, RRC Protocol Specification as the state of the art for the UMTS mobile radio system. For descriptions of the mobile radio system of the second generation GSM, the book by J. Biala, “Mobile Radio and Intelligent Networks”, Vieweg Verlag, is taken as a basis for the general state of the art.
In radio communication systems, for example the European mobile radio system of the second generation GSM (Global System for Mobile Communications), information such as speech, image information or other data are transmitted by electromagnetic waves over a radio interface. At the radio interface, one or more connections are set up between a base station and plural subscriber stations; the subscriber stations can be, for example, mobile stations or stationary radio stations. The radiation of the electromagnetic waves takes place at carrier frequencies which are situated in a frequency band provided for the respective system. For future radio communication systems, for example, the UMTS (Universal Mobile Telecommunication System) or other systems of the third generation, frequencies in the frequency band of about 2,000 MHz are provided. For the third mobile radio generation UMTS, two modes are provided, one mode being termed a FDD (Frequency Division Duplex) operation and the other mode being termed a TDD operation (Time Division Duplex) operation. These modes find their application in different frequency bands; both modes support a so-called CDMA (Code Division Multiple Access) subscriber separation method.
Based on a parallel existence and a desired harmonization between the radio communication systems of the second and third generation, subscriber stations which have set up a connection in a radio communication system are to be given the possibility of handing the connection over to a further radio communication system, which as the case may be supports another transmission mode. Such an intersystem handover assumes, besides a synchronization of the subscriber station with the radio communication system which is to take over the connection, the knowledge of the transport format used. Here, according to the referenced state of the art of base stations of the UMTS mobile radio system, a subscriber station signals, during a connection setup, a so-called set of transport format combinations TFCS (Transport Format Combination Set). With a change of the transport format used at the time, a so-called Transport Format Combination Identifier TFCI is subsequently signaled to the subscriber station, and states which transport format is used out of the set of possible transport format combinations.
The signaling of the set of transport format combinations TFCS would have a length of up to 200 8-bit bytes, depending on the number of possible TFCIs in a known GSM signaling channel. This length is very disadvantageous because of the only limited capacity available on the usable GSM signal channels.